Biodegradable polyester mixture

ABSTRACT

The invention relates to a biodegradable polyester mixture comprising:
     i) 71 to 91 wt %, based on the total weight of components i and ii, of a polyester I constructed from:
       a-1) 40 to 70 wt %, based on the total weight of components a and b, of an aliphatic C 9 -C 16  dicarboxylic acid or of a C 9 -C 16  dicarboxylic acid derivative;   b-1) 30 to 60 wt %, based on the total weight of components a and b, of terephthalic acid or of a terephthalic acid derivative;   c-1) 98 to 100 wt %, based on the total weight of components a and b, of a C 3 -C 6  diol;   d-1) 0 to 2 wt %, based on the total weight of components a and b, of an at least trihydric alcohol;   e-1) 0 to 2 wt %, based on the total weight of components a to e, of a chain extender, and   
       ii) 9 to 29 wt %, based on the total weight of components i and ii, of a polyester II constructed from:
       a-2) 40 to 70 wt %, based on the total weight of components a and b, of an aliphatic C 4 -C 6  dicarboxylic acid or of a C 4 -C 6  dicarboxylic acid derivative;   b-2) 30 to 60 wt %, based on the total weight of components a and b, of terephthalic acid or of a terephthalic acid derivative;   c-2) 98 to 100 wt %, based on the total weight of components a and b, of a C 3 -C 6  diol;   d-2) 0 to 2 wt %, based on the total weight of components a and b, of an at least trihydric alcohol;   e-2) 0 to 2 wt %, based on the total weight of components a to e, of a chain extender.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application (under 35 U.S.C. § 371)of PCT/EP2013/073339, filed Nov. 8, 2013, which claims benefit ofEuropean Application No. 12192804.8, filed Nov. 15, 2012, bothapplications of which are incorporated herein by reference in theirentirety.

The invention relates to a biodegradable polyester mixture comprising:

-   i) 71 to 91 wt %, based on the total weight of components i and ii,    of a polyester I constructed from:    -   a-1) 40 to 70 wt %, based on the total weight of components a        and b, of an aliphatic C₉-C₁₈ dicarboxylic acid or of a C₉-C₁₈        dicarboxylic acid derivative;    -   b-1) 30 to 60 wt %, based on the total weight of components a        and b, of terephthalic acid or of a terephthalic acid        derivative;    -   c-1) 98 to 100 wt %, based on the total weight of components a        and b, of a C₃-C₆ diol;    -   d-1) 0 to 2 wt %, based on the total weight of components a and        b, of an at least trihydric alcohol;    -   e-1) 0 to 2 wt %, based on the total weight of components a to        e, of a chain extender, and-   ii) 9 to 29 wt %, based on the total weight of components i and ii,    of a polyester II constructed from:    -   a-2) 40 to 70 wt %, based on the total weight of components a        and b, of an aliphatic C₄-C₆ dicarboxylic acid or of a C₄-C₆        dicarboxylic acid derivative;    -   b-2) 30 to 60 wt %, based on the total weight of components a        and b, of terephthalic acid or of a terephthalic acid        derivative;    -   c-2) 98 to 100 wt %, based on the total weight of components a        and b, of a C₃-C₆ diol;    -   d-2) 0 to 2 wt %, based on the total weight of components a to        e, of an at least trihydric alcohol;    -   e-2) 0 to 2 wt %, based on the total weight of components a to        e, of a chain extender.

BACKGROUND OF THE INVENTION

The present invention further relates to the use of these polyestermixtures.

Biodegradable polyesters such as poly(butylene adipate-co-terephthalate)(PBAT) are known from WO-A 96/015173 for example. WO-A 2010/034710describes polyesters such as poly(butylene sebacate-co-terephthalate)(PBSeT).

Biodegradability in these references refers to compostability within themeaning of DIN EN 13432. Composting in this sense relates to industrialcomposters and is to be understood as meaning that a material whenexposed for a defined period to defined temperature, oxygen and moistureconditions in the presence of microorganisms shall have degraded to morethan 90 percent into water, carbon dioxide and biomass.

Domestic garden composting generally involves a lower temperature, sogarden waste takes distinctly longer to rot down and correspondingly thedegradation rates of the plastic tested are distinctly lower. ISO 20200(2004) is an internationally standardized test for domestic gardencomposting.

DIN EN ISO 17556 was developed to determine ultimate aerobicbiodegradability in the soil. Ultimate degradation in the soil isespecially important for plastics applications in the agrisector suchas, for example, mulch films, covering films, silo films, slit filmtapes, wovens, nonwovens, clips, textiles, threads, fishing nets,secondary packaging, heavy-duty bags and flowerpots. Foam applicationsas for soil aeration must also be considered. The soil degradationperformance of polyesters described in the literature is not always upto the mark.

SUMMARY OF THE INVENTION

The present invention accordingly has for its object to provide polymersthat satisfy the material prerequisites for state-of-the-art extrusionand injection-molding applications while also having soil degradabilitywhich is improved or accelerated compared to the individual components:polyester I and polyester II.

We have found that this object is achieved by the abovementionedbiodegradable polyester mixture comprising:

-   i) 71 to 91 wt %, based on the total weight of components i and ii,    of a polyester I constructed from:    -   a-1) 40 to 70 wt %, based on the total weight of components a        and b, of an aliphatic C₉-C₁₈ dicarboxylic acid or of a C₉-C₁₅        dicarboxylic acid derivative;    -   b-1) 30 to 60 wt %, based on the total weight of components a        and b, of terephthalic acid or of a terephthalic acid        derivative;    -   c-1) 98 to 100 wt %, based on the total weight of components a        and b, of a C₃-C₆ diol;    -   d-1) 0 to 2 wt %, based on the total weight of components a and        b, of an at least trihydric alcohol;    -   e-1) 0 to 2 wt %, based on the total weight of components a to        e, of a chain extender, and-   ii) 9 to 29 wt %, based on the total weight of components i and ii,    of a polyester II constructed from:    -   a-2) 40 to 70 wt %, based the total weight of on components a        and b, of an aliphatic C₄-C₆ dicarboxylic acid or of a        dicarboxylic acid derivative;    -   b-2) 30 to 60 wt %, based on the total weight of components a        and b, of terephthalic acid or of a terephthalic acid        derivative;    -   c-2) 98 to 100 wt %, based on the total weight of components a        and b, of a C₃-C₆ diol;    -   d-2) 0 to 2 wt %, based on the total weight of components a and        b, of an at least trihydric alcohol;    -   e-2) 0 to 2 wt %, based on the total weight of components a to        e, of a chain extender.

Biodegradable films of polyester can be used as mulch films for example.The decisive requirements for this are not only tongue tear strength butalso stability to sunlight in the case of transparent mulch films inparticular. Mulch films colored black (with carbon black) already have aUV-absorbing effect, yet thermal radiation is also absorbed, which meansthat less heat gets through to the soil and the yield/harvestadvancement effect that can be achieved, at least for particular cropssuch as melons and maize, is accordingly higher.

WO 2009/071475 discloses mulch films based on polyethylene for example,which comprise hydroxyphenyltriazines as a stabilizer. Biodegradablefilms of polyester are not explicitly described in WO 2009/071475. Theservice life of biodegradable transparent mulch films based on abiodegradable polyester consisting of aliphatic and/or aromaticdicarboxylic acids and an aliphatic dihydroxy compound is often tooshort: only 2 weeks, depending on wall thickness. Light stabilizers suchas UV absorbers and HALS stabilizers, or a combination thereof, areusually recommended for the UV stabilization of mulch films. UVabsorbers work by filtering the ultraviolet portion of the light out ofthe light, so the energy of the absorbed light is converted into heat.HALS stabilizers work by suppressing the reaction of photooxidativelygenerated scission products in the polymer. When the active ingredientsreferred to are combined, a synergistic effect is achieved to inhibitthe two different mechanisms of degradation. Studies on Ecoflex® partlyaromatic polyester (BASF SE) have revealed thathydroxyphenyltriazine-based UV absorbers such as Tinuvin® 1577 usedalone or combined with a HALS stabilizer such as Tinuvin® 111 or UVabsorbers based on benzophenones such as Uvinul® 3008 do provide acertain stabilizing effect, but that this stabilizing effect issubstantially insufficient for transparent mulch films, especially atlow wall thickness.

Tongue tear strength of these mulch films is also unsatisfactory,especially in thin versions (below 30 microns).

DETAILED DESCRIPTION OF THE INVENTION

The present invention accordingly further has for its object to providebiodegradable, preferably transparent mulch films having longer servicelives in the field (above ground), higher tongue tear strength and atthe same time ultimate degradation in the soil (below ground).

We have found that this object is achieved by a polyester mixture whichin addition to components i and ii of the present invention comprisesthe UV absorber2-(4,6-bis-biphenyl-4-yl-1,3,5-triazin-2-yl)-5-(2-ethyl-(n)-hexyloxy)phenol,and is particularly useful for agricultural applications.

The present invention will now be more particularly described.

In principle, biodegradable polyester mixtures of the present inventionare obtainable using as component i any polyester I and as component iiany polyester II based on aliphatic and aromatic dicarboxylic acids andan aliphatic dihydroxy compound, which are known as partly aromaticpolyesters. A feature shared by these polyesters is the fact that theyare biodegradable within the meaning of DIN EN 13432. The essentialdifference between polyesters I and II is the chain length of aliphaticdicarboxylic acid a.

Partly aromatic polyesters (components i and ii) for the purposes of thepresent invention also include polyester derivatives comprising a smallproportion of sub-structures such as polyetheresters, polyesteramides,polyetheresteramides or polyesterurethanes. Suitable partly aromaticpolyesters include linear polyesters (WO 92/09654). Partly aromaticpolyesters that are branched and/or chain extended are preferred.Branched partly aromatic polyesters are known from the references citedabove, WO 96/15173 to 15176, 21689 to 21692, 25446, 25448 or WO98/12242, which are hereby expressly incorporated herein by reference.Mixtures of different partly aromatic polyesters are also useful.Interesting recent developments are based on renewable raw materials(see WO-A 2006/097353, WO-A 2006/097354 and WO-A 2010/034710).

Polyesters I and II of the present invention are preferably obtained bythe process described in WO 2009/127556. The process described thereinis suitable in that the gentle method of operation provides polyestersthat combine a high viscosity with a low acid number. The low acidnumber is a prerequisite for efficient reaction with diisocyanates, sothe low MVR values of the present invention are obtainable in a simpleand methodical manner. Polyesters having a melt volume rate (MVR) to ENISO 1133 (190° C., 2.16 kg weight) of 0.5 to 6.0 cm³/10 min andespecially of 0.8 to 5 cm³/10 min have proven to be particularly usefulin the manufacture of very thin films that combine tongue tear strengthwith penetration resistance.

The continuous process described in WO 2009/127556 will now be moreparticularly elucidated. For example, a mixture of 1,4-butanediol,sebacic acid, terephthalic acid and optionally further comonomers, butno catalyst, is mixed to form a paste or, alternatively, the liquidesters of the dicarboxylic acids and the dihydroxy compound andoptionally further comonomers, but no catalyst, are fed into the reactorand

-   -   1. in a first step, this mixture is continuously esterified or,        respectively, transesterified together with all or some of the        catalyst;    -   2. in a second stage, the esterification/transesterification        product obtained as per 1.) is, if appropriate together with the        rest of the catalyst, precondensed continuously—preferably in a        tower reactor where the product stream passes cocurrently over a        falling-film cascade and the reaction vapors are removed in situ        from the reaction mixture—to a DIN 53728 viscosity number of 20        to 60 mL/g;    -   3. in a third stage, the product obtainable from 2.) is        continuously polycondensed preferably in a cage reactor, to a        DIN 53728 viscosity number of 70 to 130 mL/g; and    -   4. in a fourth stage, the product obtainable from 3.) is        continuously reacted with a chain extender in a polyaddition        reaction in an extruder, a List reactor or a static mixer as far        as a DIN 53728 viscosity number of 160 to 250 mL/g.

The continuous process described in WO 2009/127556 providesaliphatic-aromatic polyesters having a DIN EN 12634 acid number of lessthan 1.0 mg KOH/g and a viscosity number of above 130 mL/g, and also anISO 1133 MVR of not more than 6 cm³/10 min (190° C., 2.16 kg weight).

Polyesters I preferably have the following construction:

-   a-1) 40 to 70 wt %, based on the total weight of components a and b,    of an aliphatic C₉-C₁₈ dicarboxylic acid or of a C₉-C₁₈ dicarboxylic    acid derivative;-   b-1) 30 to 60 wt %, based on the total weight of components a and b,    of terephthalic acid or of a terephthalic acid derivative;-   c-1) 98 to 100 wt %, based on the total weight of components a and    b, of a C₃-C₆ diol;-   d-1) 0 to 2 wt %, based on the total weight of components a and b,    of an at least trihydric alcohol;-   e-1) 0 to 2 wt %, based on the total weight of components a to e, of    a chain extender.

C₉-C₁₈ Dicarboxylic acid (component a-1) is preferably azelaic acid,sebacic acid, brassylic acid, a C₁₈ 1,18-dicarboxylic acid or thecorresponding dicarboxylic acid derivative. Sebacic acid and itsderivatives are particularly useful as component a-1. The abovementioneddiarboxylic acids these days are available from renewable raw materials.

Aliphatic dicarboxylic acid (a) and terephthalic acid (b) can be usedeither as free acid or in the form of ester-forming derivatives. Usefulester-forming derivatives include particularly the di(C₁-C₆ alkyl)esters, such as dimethyl, diethyl, di-n-propyl, diisopropyl, di-n-butyl,diisobutyl, di-t-butyl, di-n-pentyl, diisopentyl or di-n-hexyl esters.Anhydrides of dicarboxylic acids can likewise be used.

The dicarboxylic acids or their ester-forming derivatives can be usedindividually or in the form of a mixture.

In general, at the start of the polycondensation, diol (c) is adjustedrelative to the diacids (a and b) such that the ratio of diols todiacids is in the range from 1.0 to 2.5:1 and preferably in the rangefrom 1.3 to 2.2:1. Excess quantities of diol are withdrawn during thepolymerization, so an approximately equimolar ratio becomes establishedat the end of the polymerization. By “approximately equimolar” is meanta diol/diacids ratio in the range from 0.98 to 1.0:1.

Useful at least trihydric alcohols (d) include, for example,1,1,1-trimethylolpropane, 1,1,1-trimethylolethane, pentaerythritol,polyether triols and especially glycerol. Components d can be used toconstruct biodegradable polyesters i having structural viscosity. Meltrheology improves in that the biodegradable polyesters become easier toprocess, for example easier to pull into self-supporting films/sheets bymelt solidification.

Chain extenders e are polyfunctional and especially difunctionalisocyanates, isocyanurates, oxazolines, carboxylic anhydrides orepoxides.

The term “epoxides” is to be understood as meaning particularlyepoxy-containing copolymer based on styrene, acrylic ester and/ormethacrylic ester. The units which bear epoxy groups are preferablyglycidyl (meth)acrylates. Copolymers having a glycidyl methacrylatecontent of greater than 20, more preferably greater than 30 and evenmore preferably greater than 50 wt % of the copolymer will be foundparticularly advantageous. The epoxy equivalent weight (EEW) in thesepolymers is preferably in the range from 150 to 3000 and more preferablyin the range from 200 to 500 g/equivalent. The weight-average molecularweight M_(w) of the polymers is preferably in the range from 2000 to 25000 and particularly in the range from 3000 to 8000. The number averagemolecular weight M_(n) of the polymers is preferably in the range from400 to 6000 and particularly in the range from 1000 to 4000. Thepolydispersity (Q) is generally between 1.5 and 5. Epoxy-containingcopolymers of the abovementioned type are commercially available, forexample from BASF Resins B.V. under the Joncryl® ADR brand. Joncryl® ADR4368 is particularly useful as chain extender.

Useful bifunctional chain extenders e include the following compounds:

An aromatic diisocyanate comprises in particular tolylene2,4-diisocyanate, tolylene 2,6-diisocyanate, 2,2′-diphenylmethanediisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethanediisocyanate, naphthylene 1,5-diisocyanate or xylylene diisocyanate. Ofthese, particular preference is given to 2,2′-, 2,4′- and also4,4′-diphenylmethane diisocyanates. In general, the latter diisocyanatesare used as a mixture. The diisocyanates may also comprise minoramounts, for example up to 5% by weight, based on the total weight, ofurethione groups, for example for capping the isocyanate groups.

The term “aliphatic diisocyanate” herein refers particularly to linearor branched alkylene diisocyanates or cycloalkylene diisocyanates having2 to 20 carbon atoms, preferably 3 to 12 carbon atoms, for example1,6-hexamethylene diisocyanate, isophorone diisocyanate ormethylenebis(4-isocyanatocyclohexane). Particularly preferred aliphaticdiisocyanates are isophorone diisocyanate and, in particular,1,6-hexamethylene diisocyanate.

The preferred isocyanurates include the aliphatic isocyanurates whichderive from alkylene diisocyanates or cycloalkylene diisocyanates having2 to 20 carbon atoms, preferably 3 to 12 carbon atoms, for exampleisophorone diisocyanate or methylenebis(4-isocyanatocyclohexane). Thealkylene diisocyanates here may be either linear or branched. Particularpreference is given to isocyanurates based on n-hexamethylenediisocyanate, for example cyclic trimers, pentamers or higher oligomersof 1,6-hexamethylene diisocyanate.

2,2′-Bisoxazolines are generally obtainable via the process from Angew.Chem. Int. Ed., Vol. 11 (1972), pp. 287-288. Particularly preferredbisoxazolines are those in which R¹ is a single bond, a (CH₂), alkylenegroup, where z=2, 3 or 4, such as methylene, 1,2-ethanediyl,1,3-propanediyl, 1,2-propanediyl or a phenylene group. Particularlypreferred bisoxazolines are 2,2′-bis(2-oxazoline),bis(2-oxazolinyl)methane, 1,2-bis(2-oxazolinyl)ethane,1,3-bis(2-oxazolinyl)propane or 1,4-bis(2-oxazolinyl)butane, inparticular 1,4-bis(2-oxazolinyl)benzene, 1,2-bis(2-oxazolinyl)benzene or1,3-bis(2-oxazolinyl)benzene.

The number average molecular weight (Mn) of polyesters I is generally inthe range from 5000 to 100 000, particularly in the range from 10 000 to75 000 g/mol, preferably in the range from 15 000 to 50 000 g/mol, theirweight average molecular weight (Mw) is generally in the range from 30000 to 300 000, preferably 60 000 to 200 000 g/mol, and their Mw/Mnratio is generally in the range from 1 to 6, preferably in the rangefrom 2 to 4. The viscosity number is between 30 and 450 g/mL andpreferably in the range from 50 to 400 g/mL (measured in 50:50 w/wo-dichlorobenzene/phenol). The melting point is in the range from 85 to150° C. and preferably in the range from 95 to 140° C.

Polyesters I generally have a melt volume rate (MVR) to EN ISO 1133(190° C., 2.16 kg weight) of 0.5 to 10.0 cm³/10 min and preferably of0.8 to 5 cm³/10 min.

Polyesters II have the following composition:

-   a-2) 40 to 70 wt %, based on the total weight of components a and b,    of an aliphatic C₄-C₆-dicarboxylic acid or of a C₄-C₆-dicarboxylic    acid derivative;-   b-2) 30 to 60 wt %, based on the total weight of components a and b,    of terephthalic acid or of a terephthalic acid derivative;-   c-2) 98 to 100 wt %, based on the total weight of components a and    b, of a C₃-C₆ diol;-   d-2) 0 to 2 wt %, based on the total weight of components a and b,    of an at least trihydric alcohol;-   e-2) 0 to 2 wt %, based on the total weight of components a to e, of    a chain extender,

The essential difference between polyesters II and polyesters I is thechain length of the dicarboxylic acid (component a). Dicarboxylic acidcomponent a-2 has a shorter chain than dicarboxylic acid component a-1has. C₄-C₆ Dicarboxylic acid refers to succinic acid, glutaric acid andparticularly preferably adipic acid. The dicarboxylic acids succinicacid and adipic acid these days are obtainable from renewable rawmaterials. The rest of the polyester II definitions b-2, c-2, d-2 ande-2 correspond to the definitions b-1, c-1, d-1 and e-1 which were givenabove for polyester I.

Polyesters II are obtainable for example by the methods described above.Optionally, polyesters II are obtainable using less or no chain extendere. Milder reaction conditions or shorter reaction times can also beestablished in the above-described process known from WO 2009/127556 inorder that a melt volume rate (MVR) to EN ISO 1133 (190° C., 2.16 kgweight) of for example 0.5 to 10.0 cm³/10 min may be realized.

Partly aromatic polyesters II are more particularly poly(butyleneadipate-co-terephthalate) (PBAT). Commerical PBAT products such asEcoflex® F(BASF SE) and Eastar® Bio, Origo-Bi® (Novamont) are preferredpolyesters II.

The improved biodegradability in the soil is obtained in particular whenpolyester I forms the continuous or co-continuous phase in the polyestermixture of the present invention, and in particular the mixing ratio ofpolyester I to polyester II is as follows:

The polyester mixtures comprise from 71 to 91 wt %, more preferably from80 to 90 wt %, based on components i and ii, of polyester I and from 9to 29 wt %, more preferably from 10 to 20 wt %, based on components iand ii, of polyester II.

In the claimed mixing ratio, the polymer mixture of the presentinvention displays an improved DIN EN ISO 17556 soil biodegradabilityover the respective individual components: polyester I and polyester II.

The addition of polyester II to the mixtures of the present inventionfurther leads to an improvement in penetration resistance. This effectis particularly pronounced in filled polyester mixtures utilizing anadditional 5 to 25 wt %, based on the total weight of the polymermixture, of polylactic acid.

Excellent tongue tear strength and high penetration resistance isobserved with polymer mixtures comprising polyesters I having a meltvolume rate (MVR) to EN ISO 1133 (190° C., 2.16 kg weight) of 0.5 to 2.0cm³/10 min and polyesters II having a melt volume rate (MVR) to EN ISO1133 (190° C., 2.16 kg weight) of 2.5 to 10.0 cm³/10 min and from 10 to35 wt %, based on the total weight of the polymer mixture, of fillerssuch as, preferably, calcium carbonate and talc.

The polyester mixture may accordingly comprise still furtheringredients. The polyester mixture including all further ingredients ishereinbelow referred to as polymer mixture.

Calcium carbonate may be used for example at 10 to 25 wt %, preferably10 to 20 wt % and more preferably 12 to 28 wt %, based on the totalweight of the polymer mixture. Calcium carbonate from Omya will provesuitable inter alia. The average particle size of calcium carbonate isgenerally in the range from 0.5 to 10 micrometers, preferably 1-5 andmore preferably 1-2.5 micrometers.

Talc may be used for example at 3 to 15 wt %, preferably 5 to 10 wt %and more preferably 5 to 8 wt %, based on the total weight of thepolymer mixture, Talc from Mondo Minerals will be found suitable interalia. The average particle size of talc is generally 0.5-10, preferably1-8 and more preferably 1-3 micrometers.

Still further minerals may be present in addition to the fillers calciumcarbonate and talc: graphite, gypsum, carbon black, iron oxide, calciumchloride, kaolin, silicon dioxide (quartz), sodium carbonate, titaniumdioxide, silicate, wollastonite, mica, montmorillonites, mineral fibersand natural fibers.

Natural fibers are generally cellulose fibers, kenaf fibers, hempfibers, wood flour or potato peel. They are preferably used at 1 to 20wt % based on the polymer mixture.

The minerals including the fillers calcium carbonate and talc can alsobe used in the form of nanofillers. Nanofillers are particularly finelydivided sheet-silicates, preferably clay minerals and more preferablyclay minerals comprising montmorillonite, the surface of which ismodified with one or more quaternary ammonium salts and/or phosphoniumsalts and/or sulfonium salts. Natural montmorillonites and bentonitesare preferred clay minerals.

Altogether, the polyester mixtures may comprise for example fillers at10 to 35 wt %, based on the total weight of the polymer mixture.

In a preferred embodiment, the polyester mixtures may have added to themstill further polymers selected from the group consisting of polylacticacid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate, starch orpolyester prepared from aliphatic dicarboxylic acids and an aliphaticdihydroxy compound.

Polylactic acid is preferably added at 5 to 25 wt % and more preferablyat 6 to 12 wt %, based on the total weight of the polymer mixture.

The use of PLA having the following range of properties is preferred:

-   -   a melt volume rate (MVR) to EN ISO 1133 (190° C., 2.16 kg        weight) of 0.5 to 30 especially 2 to 40 cm³/10 min;    -   a melting point below 240° C.;    -   a glass transition temperature (Tg) above 55° C.;    -   a water content of below 1000 ppm;    -   a residual (lactide) monomer content of below 0.3%;    -   a molecular weight of above 80 000 daltons.

Examples of preferred polylactic acids are Ingeo® 8052D, 6201 D, 6202D,6251 D, 3051 D and especially Ingeo® 4020D, 4032D or 4043D polylacticacid (from NatureWorks).

Adding PLA in the claimed proportion provides a further distinctimprovement in the properties of the polyester film (penetrationresistance and tongue tear strength) obtained from the polymer mixture.Mixtures of easy-flowing and more viscous PLA can also be used.

Aliphatic polyesters may further preferably be used at 5 to 45 wt %,based on the total weight of the polymer mixture.

The term “aliphatic polyesters” also comprehends polyesters formed fromaliphatic diols and aliphatic dicarboxylic acids such as polybutylenesuccinate (PBS), polybutylene adipate (PBA), polybutylene succinateadipate (PBSA), polybutylene succinate sebacate (PBSSe), polybutylenesebacate (PBSe) or corresponding polyesters having a polyesteramide orpolyesterurethane sub-structure. Aliphatic polyesters are marketed forexample by the companies Showa Highpolymers and Mitsubishi under thenames Bionolle and GSPIa respectively. More recent developments aredescribed in WO-A 2010/034711.

Similar effects are found on adding from 10 to 35 wt %, based on thetotal weight of the polymer mixture, of a polyhydroxyalkanoate or starchto the polyester films.

Polyhydroxyalkanoates are primarily poly-4-hydroxybutyrates andpoly-3-hydroxybutyrates and copolyesters of the aforementionedpolyhydroxybutyrates with 3-hydroxyvalerate, 3-hydroxyhexanoate and/or3-hydroxyoctanoate. Poly-3-hydroxybutyrates are available for examplefrom PHB Industrial under the tradename Biocycle® and from Tianan underthe name Enmat®.

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)s are known from Metabolixin particular. They are marketed under the brand name Mirel®.

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)s are known from P&G orKaneka. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)s generally have a3-hydroxyhexanoate content of 1 to 20 and preferably 3 to 15 mol % basedon the polyhydroxyalkanoate. The molecular weight Mw ofpolyhydroxyalkanoates is generally in the range from 100 000 to 1 000000 and preferably in the range from 300 000 to 600 000.

Starch also comprehends amylose; thermoplasticized is to be understoodas meaning surface modified (see EP-A 937120, EP-A 947559, EP-A 965615)or else thermoplasticized with plasticizers such as glycerol, sorbitolor water for example (see EP-A 539 541, EP-A 575 349, EP-A 652 910).Polymer mixtures of the present invention that comprise that comprise 10to 35 wt. %, based on the total weight of the polymer mixture, ofthermoplastic or non thermoplastic starch exhibit not only effectivesoil degradability but also good mechanical properties such as, inparticular, high tongue tear strength. These starch-containing mixturesare therefore an interesting alternative to the aforementionedfiller-containing mixtures (containing calcium and/or talc), optionallyalso in combination with the filler-containing polymer mixtures.

The polyester film of the present invention may further comprise furtheradditives known to a person skilled in the art, for example thematerials customarily added in plastics technology such as stabilizers;nucleating agents; glide and release agents such as stearates(especially calcium stearate); plasticizers such as, for example, citricesters (particularly tributyl acetylcitrate), glyceric esters such astriacetylglycerol or ethylene glycol derivatives, surfactants such aspolysorbates, palmitates or laurates; waxes such as, for example,erucamide, stearamide or behenamide, beeswax or beeswax esters;antistat, UV absorbers; UV stabilizers; antifoggants; or dyes. Theadditives are used at concentrations of 0 to 2 wt %, especially 0.1 to 2wt % based on the polyester film of the present invention. Plasticizersmay be present in the polyester film of the present invention at 0.1 to10 wt %.

By way of UV absorber it is preferable to use from 0.1 to 1.5 wt % andmore preferably from 0.5 to 1.2 wt %, based on the total weight of thepolymer mixture, of2-(4,6-bis-biphenyl-4-yl-1,3,5-triazin-2-yl)-5-(2-ethyl-(n)-hexyloxy)phenol.Preparation and properties of said UV absorber vi are known from WO2009/071475. WO 2009/071475 is hereby expressly incorporated in thiscontext by reference.

The polymer mixtures, especially the mixtures comprising polylacticacid, may also incorporate from 0 to 1 wt %, preferably from 0.01 to 0.8wt % and more preferably from 0.05 to 0.5 wt %, based on the totalweight of components i to vi, of an epoxy-containing copolymer based onstyrene, acrylic ester and/or methacrylic ester. The units which bearepoxy groups are preferably glycidyl (meth)acrylates. Copolymers havinga glycidyl methacrylate content of above 20, more preferably of above 30and even more preferably of above 50 wt % of the copolymer will be foundparticularly advantageous. The epoxy equivalent weight (EEW) of thesepolymers is preferably in the range from 150 to 3000 and more preferablyin the range from 200 to 500 g/equivalent. The weight-average molecularweight M_(w) of the polymers is preferably in the range from 2000 to 25000 and particularly in the range from 3000 to 8000. The number-averagemolecular weight M_(n) of the polymers is preferably in the range from400 to 6000 and particularly in the range from 1000 to 4000. Thepolydispersity (Q) is generally in the range between 1.5 and 5.Epoxy-containing copolymers of the abovementioned type are commerciallyavailable, for example from BASF Resins B.V. under the Joncryl® ADRbrand. Joncryl® ADR 4368 is particularly suitable. Component v is usedin PLA-containing polyester mixtures in particular.

A preferred embodiment is directed to biodegradable polyester mixturesof the following composition:

-   i) 71 to 91 wt %, preferably 80 to 90 wt %, based on components i    and ii, of a polyester I;-   ii) 9 to 29 wt %, preferably 10 to 20 wt %, based on components i    and ii, of a polyester II;-   iii) 0 to 25 wt %, preferably 10 to 25 wt %, based on the total    weight of the components i to vi, of calcium carbonate;-   iv) 0 to 15 wt %, preferably 3 to 10 wt %, based on the total weight    of components i to vi, of talc;-   v) 0 to 50 wt %, preferably 5 to 45 wt %, based on the total weight    of components i to vi, of one or more polymers selected from the    group consisting of polylactic acid, polycaprolactone,    polyhydroxyalkanoate, starch or polyester prepared from aliphatic    dicarboxylic acids and an aliphatic dihydroxy compound; particular    preference is given to the range from 5 to 25 wt %, based on the    total weight of components i to vi, of polylactic acid;-   vi) 0 to 2 wt %, preferably 0.1 to 1.5 wt %, based on the total    weight of components i to vi, of one or more stabilizer, nucleating    agent, glide and release agent, surfactant, wax, antistat,    antifoggant, dye, pigment, UV absorber, UV stabilizer or other    plastics additive, particular preference being given to the    UV-absorber    2-(4,6-bis-biphenyl-4-yl-1,3,5-triazin-2-yl)-5-(2-ethyl-(n)-hexyloxy)phenol.

For the purposes of the present invention, a polymer mixture satisfiesthe “biodegradable in soil” feature when, in accordance with DIN EN ISO17556, its percentage degree of biodegradation in 2 years is not lessthan 90%. It is additionally necessary to test the eco-toxicology of theproducts used and to comply with the heavy-metal limits (see Vicotte's“ok biodegradable soil” certification). Ultimate aerobic biodegradationin soil can be measured by measuring the oxygen requirements in arespirometer or the amount of carbon dioxide generated—absolutely orrelatively to cellulose.

The general effect of biodegradability is that the polyesters orpolyester mixtures are converted into carbon dioxide, water and biomasswithin a reasonable and verifiable interval. Degradation may be effectedenzymatically, hydrolytically, oxidatively and/or through agency ofelectromagnetic radiation, for example UV radiation, and may bepredominantly due to the agency of microorganisms such as bacteria,yeasts, fungi and algae.

Biodegradability in the sense of compostability is quantifiable, forexample, by polyesters being mixed with compost and stored for a certainlength of time. According to DIN EN 13432 (which makes reference to ISO14855) for example, CO₂-free air is flowed through ripened compostduring composting and the ripened compost subjected to a definedtemperature program. Biodegradability here is defined via the ratio ofthe net CO₂ release from the sample (after deduction of the CO₂ releasedby the compost without sample) to the maximum amount of CO₂ releasableby the sample (reckoned from the carbon content of the sample), as apercentage degree of biodegradation. Biodegradable polyesters/polyestermixtures typically show clear signs of degradation, such as fungalgrowth, cracking and holing, after just a few days of composting. Othermethods of determining biodegradability are described in ASTM D 5338 andASTM D 6400-4 for example.

The biodegradable polyester mixtures referred to at the beginning areuseful in the manufacture of nets and wovens, tubular film, chill rollfilm with and without orientation in a further operation, with andwithout metallization or SiOx coating.

The polyester mixtures defined at the beginning, comprising componentsi) to vi), are particularly useful for tubular film and stretch wrappingfilm. Possible applications here are bottom gusset bags, side seam bags,grip hole carrier bags, shrink labels or vest type carrier bags,inliners, heavy-duty bags, freezer bags, composting bags, agriculturalfilm (mulch film), film bags for packaging food items, peelable closurefilm—transparent or opaque—weldable closure film—transparent oropaque—sausage casing, salad film, keep-fresh film (stretch wrappingfilm) for fruit and vegetables, meat and fish, stretch wrapping film forwrapping pallets, film for nets, packaging film for snacks,confectionary bars and muesli bars, peelable lid films for dairypackaging (yogurt, cream, etc.), fruit and vegetables, semi-rigidpackaging for smoked sausage and for cheese.

Single- or multi-ply tubular, cast or press film extruded from thepolyester mixtures comprising components i to vi) have a distinctlyhigher tongue tear strength (as per EN ISO 6383-2:2004) than whenextruded from mixtures without components ii to v). Tongue tear strengthis a very important property of products particularly in the field ofthin (tubular) film for, for example, biowaste bags or thin-wall carrierbags (e.g., vest type carrier bags, fruit bags). Tongue tear strength isalso very important for mulch film in the agrisector.

The polyester mixtures comprising components i to vi) are also usefulfor foam applications such as, for example, for soil aeration, forflowerpots or for receptacles for seedlings.

Polyester films comprising UV absorber (vi)2-(4,6-bis-biphenyl-4-yl-1,3,5-triazin-2-yl)-5-(2-ethyl-(n)-hexyloxy)phenolare more particularly used for applications which are destined for theoutdoor sector such as building construction and especially foragriproducts. Agriproducts are mulch films, covering films, silo films,slit film tapes, wovens, nonwovens, clips, textiles, threads, fishingnets, secondary packaging, such as heavy-duty bags for, for example,peat, fertilizer, cement, crop protection agents, seed or flowerpots.

Agriproducts are generally exposed to wind and weather and especiallysunlight. They have to be stabilized to ensure a defined service life inthe field.

Performance-related measurements:

Molecular weights Mn and Mw of partly aromatic polyesters weredetermined as per DIN 55672-1 using hexafluoroisopropanol (HFIP)+0.05 wt% of potassium trifluoroacetate for elution. Narrowly distributedpolymethyl methacrylate standards were used for calibration. Viscositynumbers were determined according to DIN 53728 Part 3, Jan. 3, 1985,Capillary viscometry. An M-II type Ubbelohde microviscometer was used.The solvent used was 50/50 (w/w) phenol/o-dichlorobenzene.

Describe method used to determine MVR (necessary particulars/differencesregarding implementation of EN ISO 1133 (190° C., 2.16 kg weight)).

Tongue tear strength was determined via an Elmendorf test as per EN ISO6383-2:2004 on test specimens of constant radius (43 mm tear length)using a ProTear instrument.

Modulus of elasticity and elongation at break were determined in an ISO527-3 tensile test on blown film about 30 μm in thickness.

ASTM D 1709 dart drop test method A was applied to film 30 μm inthickness to determine the maximum energy needed for the dart droppingonto the film to pass through the film. This energy is expressed interms of the weight of the dart in g which is dropped onto the film froma certain height and leads to a 50 percent failure (see ASTM in annex).

Degradation rates of biodegradable polyester mixtures and of comparativemixtures were determined in accordance with DIN EN ISO 17556 (Dec. 1,2012):

During the aerobic biodegradation, the substrate was converted intocarbon dioxide, water and biomass by microbial activity. The test methoddescribed here permits quantitative tracking of the biodegradation ofpolymer samples in soil.

The inoculum consisted of a mixture of natural soils after removal ofcoarse constituents with a 2 mm sieve. The water content of the inoculumwas adjusted to 40-60% of the maximum water-holding capacity of the soilmixture. The pH was between 6 and 8, more particularly equal to 7.2. Thepolymer sample (powder) was directly mixed with the inoculum (1 g ofpolymer per 500 g of soil) and placed in the reactor. The reactorcontained not only a vessel with potassium hydroxide solution to absorbthe generated carbon dioxide but also a vessel with water to preventdrying out of the soil. The reactor was sealed airtight and stored inthe dark at 25° C.

The amount of generated carbon dioxide was determined by titration.After every titration, the potassium hydroxide solution was renewed andthe soil commixed and, if necessary, moistened.

Biodegradation was computed from the amount of carbon dioxide generated.For this, it was merely necessary to allow for the background emission(carbon dioxide production of the inoculum without polymer sample: blanktest) and to know the total organic carbon (TOC) content of the polymersample.

I. Materials Used:

-   i-1 Poly(butylene sebacate-co-terephthalate)

Dimethyl terephthalate (70.11 kg), 1,4-butanediol (90.00 kg), glycerol(242.00 g), tetrabutyl orthotitanate (TBOT) (260.00 g) and sebacic acid(82.35 kg) were initially charged to a 250 L tank and the apparatus waspurged with nitrogen. Methanol was distilled off up to an internaltemperature of 200° C. After cooling down to about 160° C., the mixturewas condensed in vacuo (<5 mbar) at up to an internal temperature of250° C. Attainment of the desired viscosity was followed by cooling toroom temperature. The prepolyester had a viscosity number of 80 mL/g.

Chain extension was carried out in a Rheocord 9000 Haake kneader havinga Rheomix 600 attachment. The prepolyester was melted at 220° C. and themelt was admixed with 0.9 wt %, based on polyester I, of HDI(hexamethene diisocyanate) by dropwise addition. Reaction progress wastracked by observing the torque. The reaction mixture was cooled downafter attainment of the maximum torque, and the chain-extendedbiodegradable polyester was removed and characterized. Polyester i-1 hadan MVR of 1.0 cm³/10 min.

-   i-2 Poly(butylene sebacate-co-terephthalate)

The prepolyester was prepared similarly to Example 1 and admixed with0.3 wt % of HDI (hexamethene diisocyanate). Polyester i-2 had an MVR of4.6 cm³/10 min.

-   ii-1 Poly(butylene adipate-co-terephthalate)

To prepare polyester ii-1, 87.3 kg of dimethyl terephthalate, 80.3 kg ofadipic acid, 117 kg of 1,4-butanediol and 0.2 kg of glycerol were mixedtogether with 0.028 kg of tetrabutyl orthotitanate (TBOT), the molarratio between the alcohol components and the acid component being 1.30.The reaction mixture was heated to a temperature of 180° C. and reactedat that temperature for 6 h. The temperature was subsequently raised to240° C. and excess dihydroxy compound was distilled off in vacuo over aperiod of 3 h. This was followed by the gradual metered addition at 240°C. of 0.9 kg of hexamethylene diisocyanate in the course of 1 h.

Polyester ii-1 thus obtained had a melting temperature of 119° C. and anMVR of 3.1 cm³/10 min.

-   iii-1) Calcium carbonate of the type “Omyafilm 764 OM” from OMYA-   iv-1) Talc of the type “Microtalk IT extra” from Mondo Minerals-   v-1) Polylactic acid (PLA) Ingeo® 4043D from Natureworks LLC-   vi-1) Batch A: 20 wt % masterbatches of Joncryl ADR 4368 in    polyester ii-1 (see EP-A 1838784 for preparation)    II. Compounding

The polymer mixtures of Examples 1 to 4 and Comparative Examples V1 toV3a were mixed in the quantitative ratios reported in Tables 1 and 2 andcompounded on a Coperion ZSK40 MC extruder with L/D 44 and 11 zones. Thebarrel temperatures are between 180 and 210° C. and melt temperature isbetween 240 and 270° C. Components i-1, ii-1, optionally v-1 and vi-1were cold-fed into zone 1, component iii-1 was optionally side-fed intozone 8 and component iv-1 was optionally side-fed into zone 5. Screwspeed, throughput and all other process parameters were appropriatelyoptimized for the compounds.

III. Film Production:

Blown Film Line

The tubular film line was operated with a 25 D length extruder having a30 mm screw and equipped with a smooth feed section and a three-zonescrew. The feed section was cooled with about 10-15 kg/h of cold waterat maximum throughput. Zone temperatures were chosen such that melttemperature was between 170 and 190° C. Die temperatures were in therange of 160-180° C. Die diameter was 80 mm, die width was 0.8 mm. Theblow-up ratio of 3.5:1 resulted in a lay-flat width of about 440 mm forthe tubular film.

IV. Results

TABLE 1 Soil degradation of ground polymeric powders according to DIN ENISO 17556 measured by carbon dioxide generated Cellulose Example 1 V3 V4V5 V1 V2 (reference) i-1 [wt. %] 90 70 50 10 100 ii-1 [wt. %] 10 30 5090 100 Particle size 100-300 μm <100 μm Degradation after 120 days 46.1%32.7% 23.4% 3.3% 42.4% 1.7%* 80.0% Maximum expected 38.2% 29.7% 21.2%4.2% — — — degradation after 120 days (assumption: only i-1 contributesmeasurably to degradation) Difference between +7.9% +3.0% +2.2% 0.9% — —— measured and expected degradation *Degradation outcome after 118 days,carried out under the conditions described on page 18 (only smallerparticle size) according to DIN EN ISO 17556.

Table 1 shows the degradation of polyester I and polyester II and alsothe degradation of mixtures of polyesters I and II in the soil accordingto DIN EN ISO 17556. Whereas the pure polyester I exhibits degradationof 42.4% after 120 days, there is virtually no degradation of the purepolyester II in the soil. Even more surprising was that the inventivemixture of 90 wt % polyester I and 10 wt % polyester II (example 1) infact degrades more quickly in the soil than the pure polyester I. It isseen, furthermore, that up to a fraction of 50 wt. % polyester II thedegradation figure is above the arithmetically anticipated maximumdegradation figure (i.e., degradation of polyester I [VI]* fraction ofpolyester I in the mixture), but no longer above that of the polyesterI. For the polymer mixtures of the present invention, there is asurprising synergistic degradation behaviour.

TABLE 2 Soil degradation of ground polymeric powders according to DIN ENISO 17556 measured by carbon dioxide generated Example Cellulose 2 V1-a(reference) i-1 [wt %] 52.5 71.5 i-2 [wt %] — — ii-1 [wt %] 19 — ii-1proportion* 26.6 0 iii-1 [wt %] 14 14 iv-1 [wt %] 6 6 v-1 [wt %] 8 8vi-1 [wt %] 0.5 0.5 Particle size <100 μm Degradation after 58.30%45.50% 86.2% 180 days *proportion of component ii-1 as a proportion ofthe total weight of components i and ii

Polyesters I have good soil degradability in comparison with polyestersII. It was all the more surprising that the inventive mixture of apolyester I and a polyester II degrades even distinctly faster in soilthan polyester I and hence has superior soil degradability to either ofthe two individual components.

TABLE 3 Tongue tear strength and dart drop of film 30 μm in thicknessExample 3 4 5 V6 V2-a V1-b i-1 [wt %] 64.35 57.2 52.5 28.6 — i-2 [wt %]— — — — 71.5 ii-1 [wt %] 7.15 14.3 19 42.9 71.5 — ii-1 10 20 26.6 60 1000 proportion* iii-1 [wt %] 14 14 14 14 14 14 iv-1 [wt %] 6 6 6 6 6 6 v-1[wt %] 8 8 8 8 8 8 vi-1 [wt %] 0.5 0.5 0.5 0.5 0.5 0.5 Film thickness 3030 30 30 30 30 [μm] Tongue tear 6052 5815 5948 3321 1743 4154 strengthat 800 g along [mN] across [mN] 4772 3499 3615 1660 1933 5937 Dart drop172.5 194.3 184.5 208.5 304.5 153.0 method A [g] *proportion ofcomponent ii-1 as a proportion of the total weight of components i andii

The tests show that filled polyesters H (see V2-a) have very goodpenetration resistance (dart drop), while filled polyesters I (see V1-b)have very good tongue tear strength. The polyester mixtures of thepresent invention (see Examples 3 to 5) have both very good tongue tearstrength and good penetration resistance (dart drop).

We claim:
 1. A biodegradable polyester mixture comprising: i) 80 to 90wt %, based on the total weight of components i and ii, of a polyester Iconstructed from: a-1) 40 to 70 mol %, based on components a and b, ofsebacic acid or sebacic acid derivative; b-1) 30 to 60 mol %, based oncomponents a and b, of terephthalic acid or of a terephthalic acidderivative; c-1) 98 to 100 mol %, based on components a and b, of a1,4-butane diol; d-1) 0 to 2 wt %, based on the total weight ofcomponents a to e, of an at least trihydric alcohol; e-1) 0 to 2 wt %,based on the total weight of components a to e, of a chain extender, andii) 10 to 20 wt %, based on the total weight of components i and ii, ofa polyester II constructed from: a-2) 40 to 70 mol %, based oncomponents a and b, of adipic acid or adipic acid derivative; b-2) 30 to60 mol %, based on components a and b, of terephthalic acid or of aterephthalic acid derivative; c-2) 98 to 100 mol %, based on componentsa and b, of a 1,4-butane diol; d-2) 0 to 2 wt %, based on the totalweight of components a and b, of an at least trihydric alcohol; e-2) 0to 2 wt %, based on the total weight of components a to e, of a chainextender.
 2. The biodegradable polyester mixture according to claim 1further comprising 10 to 35 wt %, based on the total weight of thepolymer mixture, of one or more fillers selected from the groupconsisting of calcium carbonate, talc, graphite, gypsum, carbon black,iron oxide, calcium chloride, kaolin, silicon dioxide (quartz), sodiumcarbonate, titanium dioxide, silicate, wollastonite, mica,montmorillonites, mineral fibers and natural fibers.
 3. Thebiodegradable polyester mixture according to claim 2 wherein calciumcarbonate and/or talc are used as fillers.
 4. The biodegradablepolyester mixture according to claim 3 wherein the calcium carbonate ispresent from 10 to 25 wt %, and the talc is present from 3 to 10 wt %,based on the total weight of the polymer mixture.
 5. The biodegradablepolyester mixture according to claim 1 further comprising 5 to 50 wt %,based on the total weight of the polymer mixture, of one or morepolymers v) selected from the group consisting of polylactic acid,polycaprolactone, polyhydroxyalkanoate, starch or polyester preparedfrom aliphatic dicarboxylic acids and an aliphatic dihydroxy compound.6. The biodegradable polyester mixture according to claim 1 furthercomprising 5 to 45 wt %, based on the total weight of the polymermixture, of polycaprolactone (PCL) or of an aliphatic polyester selectedfrom the group consisting of polybutylene succinate (PBS), polybutyleneadipate (PBA), polybutylene succinate adipate (PBSA), polybutylenesuccinate sebacate (PBSSe), polybutylene sebacate (PBSe), polyethylenesuccinate (PES) and polycaprolactone (PCL).
 7. The biodegradablepolyester mixture according to claim 1 further comprising 5 to 45 wt %,based on the total weight of the polymer mixture, of starch and/or of apolyhydroxyalkanoate.
 8. The biodegradable polyester mixture accordingto claim 1 further comprising from 5 to 25 wt %, based on the totalweight of the polymer mixture, of polylactic acid.
 9. The biodegradablepolyester mixture according to claim 1 utilizing from 0.1 to 1.5 wt %,based on the total weight of the polymer mixture, of one or more thanone stabilizer, nucleating agent, glide and release agent, surfactant,wax, antistat, antifoggant, dye, pigment, UV absorber, UV stabilizer orother plastics additive.
 10. A plastic bag or inliner for a biowastebin, the bag or the inliner prepared from the polyester mixtureaccording to claim
 1. 11. An agriproduct manufactured from the polyestermixture according to claim 1, the agriproducts selected from the groupconsisting of mulch films, covering films, bead foam for soil aeration,silo films, slit film tapes, wovens, nonwovens, clips, textiles,threads, fishing nets, secondary packaging, heavy-duty bags andflowerpots.
 12. The biodegradable polyester mixture according to claim1, comprising poly(butylene sebacate-co-terephthalate) (PBSeT) andpoly(butylene adipate-co-terephthalate) (PBAT).
 13. A biodegradablepolyester mixture comprising: i) 80 to 90 wt %, based on the totalweight of components i and ii, of a polyester I constructed from: a-1)40 to 70 mol %, based on components a and b, of sebacic acid or asebacic acid derivative; b-1) 30 to 60 mol %, based on components a andb, of terephthalic acid or of a terephthalic acid derivative; c-1) 98 to100 mol %, based on components a and b, of a C₃-C₆ diol; and ii) 10 to20 wt %, based on the total weight of components i and ii, of apolyester II constructed from: a-2) 40 to 70 mol %, based on componentsa and b, is adipic acid or an adipic acid derivative; b-2) 30 to 60 mol%, based on components a and b, of terephthalic acid or of aterephthalic acid derivative; c-2) 98 to 100 mol %, based on componentsa and b, of a 1,4-butane diol; and iii) 10 to 35 wt %, based on thetotal weight of the polymer mixture, of one or more fillers selectedfrom calcium carbonate, talc or a mixture thereof.
 14. The biodegradablepolyester mixture according to claim 13 further comprising 5 to 45 wt %,based on the total weight of the polymer mixture, of polycaprolactone(PCL) or of an aliphatic polyester selected from the group consisting ofpolybutylene succinate (PBS), polybutylene adipate (PBA), polybutylenesuccinate adipate (PBSA), polybutylene succinate sebacate (PBSSe),polybutylene sebacate (PBSe), polyethylene succinate (PES) andpolycaprolactone (PCL).
 15. The biodegradable polyester mixtureaccording to claim 13 further comprising 5 to 45 wt %, based on thetotal weight of the polymer mixture, of starch and/or of apolyhydroxyalkanoate.
 16. The biodegradable polyester mixture accordingto claim 15 further comprising from 5 to 25 wt %, based on the totalweight of the polymer mixture, of polylactic acid.
 17. The biodegradablepolyester mixture according to claim 12, comprising 90 wt % PBSeT and 10wt. % PBAT.